The present invention relates to a controller for a hydraulic pump, and more particularly to a hydraulic pump controller suitable for use with hydraulic construction machines.
Generally, the power unit system (hydraulic system) of a hydraulic construction machine is equipped with one or a plurality of variable displacement type hydraulic pumps which are driven by engine power. For example, a hydraulic system for a hydraulic shovel that is a typical hydraulic construction machine is equipped with first and second variable displacement type hydraulic pumps 9 and 10 which are driven by power from an engine 11, as shown in FIG. 12. The discharge pressure oil from these hydraulic pumps 9 and 10 is supplied to a plurality of hydraulic actuators 27 and 28 through direction switching valves 15 and 17 where the opening degree varies according to the amount that manipulation levers 19 and 20 are manipulated. To supply adequate amount of pressure oil to the hydraulic actuators 27 and 28 that are compositely manipulated, it is necessary to control absorbed pump torque in good balance against engine output so that an actual engine speed can follow a target engine speed.
Hence, the hydraulic system is equipped with a controller 30 to which sensor signals are input from an engine speed sensor 22 and a pressure switch 31. In the controller 30, the engine speed of an engine 11 is detected based on an input signal from the engine speed sensor 22, and it is decided, based on an input signal from the pressure sensor 31, whether or not the hydraulic pumps 9 and 10 are discharging pressure oil. And to control the absorbed torque (or absorbed horse power) of the hydraulic pumps 9 and 10 so that the engine speed follows the target engine speed, a control signal Ps is output to regulators 12 and 13 that regulate the discharge flow rates of the hydraulic pumps 9 and 10. In an electromagnetic proportional pressure-reducing valve 14, electro-oil conversion is performed on the control signal Ps, and the converted signal is input to the regulators 12 and 13.
The aforementioned conventional hydraulic-pump controller, however, cannot predict changes in the discharge flow rates of the hydraulic pumps 9 and 10 caused by manipulation of the manipulation levers 19 and 20. Because of this, when the discharge flow rates of the hydraulic pumps 9 and 10 are transiently changed, for example, immediately after manipulation of the manipulation levers 19 and 20, or during slight manipulation, the balance between engine output and absorbed pump torque will be lost and a fluctuation in an actual engine speed relative to a target engine speed will become great. As a result, adequate amount of pressure oil cannot be supplied to the hydraulic actuators 27 and 28, and operability is degraded.
Further, with the conventional hydraulic-pump controller, it is necessary to perform tuning of control parameters in accordance with the type of the hydraulic shovels. That is, there is a need to amend part of the control program for each hydraulic shovel type. Besides, there is an individual difference between hydraulic shovels, even if they are of the same type. Furthermore, there are cases where working environment varies, for example, between a cold district and a warm district, and where engine fuel is changed. Thus, if individual difference, working environment, and conditions vary, tuning of control parameters, performed before shipping hydraulic shovels, will no longer be adaptable and therefore a fluctuation in an actual engine speed relative to a target engine speed will become great and will degrade operability.
The present invention has been made in view of such problems. Accordingly, it is an object of the present invention to provide a hydraulic-pump controller that is capable of controlling absorbed pump torque in good balance against engine output at all times.
Another object of the invention is to provide a hydraulic-pump controller which eliminates the necessity of tuning control parameters and amending a control program, even in the case where there is an individual difference between hydraulic construction machines, or the case where working environment varies, or the case where it is installed in a different type of hydraulic construction machine.
In accordance with the present invention, there is provided a hydraulic-pump controller which is equipped in a hydraulic system, in which hydraulic pumps are driven by an engine so that operating oil is supplied to hydraulic actuators manipulated by manipulation means, and which also controls regulators of the hydraulic pumps so that absorbed torque of the hydraulic pumps balances with an output of the engine, the hydraulic-pump controller comprising:
engine speed detection means for detecting engine speed of the engine;
discharge pressure detection means for detecting discharge pressure of the hydraulic pumps;
manipulation-amount detection means for detecting an amount that the manipulation means is manipulated, or a physical quantity correlating with the amount;
discharge flow rate predicting means for predicting discharge flow-rates of the operating oil which are discharged from the hydraulic pumps according to manipulation of the manipulation means, based on an output of the discharge pressure detection means and an output of the manipulation-amount detection means;
predictive engine speed computing means for calculating the absorbed torque of the hydraulic pumps, based on the discharge flow rates predicted by the discharge flow rate predicting means and an output of the discharge pressure detection means, and then computing a predictive engine speed of the engine from the calculated absorbed torque of the hydraulic pumps; and
regulator control means for controlling the regulators, based on a deviation between the predictive engine speed computed by the predictive engine speed computing means and an actual engine speed detected by the engine speed detection means.
With this construction, the discharge flow rates of the operating oil, that are discharged from the hydraulic pumps being operated can be predicted according to manipulation of the manipulation means, based on the discharge pressure of the hydraulic pumps, and based on the manipulation amount of the manipulation means, or a physical quantity correlating with the manipulation amount. Therefore, it is possible to make the actual engine speed of the engine follow the predictive engine speed, without losing the balance between the engine output and the absorbed pump torque, immediately after lever manipulation, or during slight manipulation. Thus, the hydraulic-pump controller of the present is capable to of preventing operability degradation due to engine speed fluctuations.
In a preferred form of the present invention, the regulator control means is a means for controlling the regulators by employing fuzzy reasoning. The regulator control means includes conformability computing means for setting a plurality of antecedent conditions in accordance with a range of operating states of the hydraulic system and then computing conformability of each antecedent condition relative to physical quantities representing the operating states, and learning-correction means for setting a plurality of control parameters for controlling the regulators, in accordance with the antecedent conditions, and for learning and correcting each of the control parameters, based on both the deviation between the predictive engine speed and the actual engine speed and the conformability of each antecedent condition computed by the conformability computing means, and then outputting the corrected control parameters to the regulators.
Thus, the hydraulic-pump controller is robust in control, because it employs fuzzy reasoning to control the regulators. In addition, based on the conformability of each antecedent condition relative to a quantity representing the operating state of the hydraulic system, and based on the deviation between the actual engine speed and the predictive engine speed, the control parameters are learned and corrected and are output to the regulators. Thus, the hydraulic-pump controller is capable of manipulating the absorbed torque of the hydraulic pumps according to the output states of the hydraulic pumps and the response of the engine speed. Even in the case where the operating state of the hydraulic system varies, for instance, there is an individual difference between hydraulic construction machines, or the case where working environment varies, and furthermore, even in the case where it is installed in a different type of hydraulic construction machine, the hydraulic-pump controller is capable of eliminating the tuning of the control parameters and the operation to change a control program.
In another preferred form of the present invention, the discharge pressure and the discharge flow rates are treated as the physical quantities representing the operating states, and the antecedent conditions are set in accordance with the discharge pressure and the discharge flow rates. In still another preferred form of the present invention, a first-order differentiated value and a second-order differentiated value of the predictive engine speed are treated as the physical quantities representing the operating states, and the antecedent conditions are set in accordance with the first-order differentiated value and the second-order differentiated value.